The present invention relates to the production of silane from halogenated silanes, and especially to the reaction of an alkali metal hydride with a silicon halide to form silane and an alkali metal halide.
The reaction of an alkali metal hydride with a silicon halide to form silane and alkali metal halide is described in British Pat. No. 909,950, published Nov. 7, 1962. The reference indicates that the reaction proceeds in the presence of certain zinc-containing salts and in the presence of certain ethers which have appreciable solvent action for the halogen-substituted silane compound. The reference gives examples of reactions of silicon tetrachloride and various other chlorosilanes and bromosilanes, but not fluorosilanes. Examples given of suitable ethers are tetrahydrofuran, diethyleneglycol dimethyl ether, ethyleneglycol dimethyl ether, 1,4-dioxane, diethyl ether, dipropyl ether, diisopropyl ether, triethyleneglycol dimethyl ether, tetraethyleneglycol dimethyl ether and dichlorodiethyl ether.
There are also limited disclosures in the art of the conversion of silicon tetrafluoride to silane using either calcium hydride or lithium aluminum hydride. Only the lithium aluminum hydride reaction is reported to result in complete conversions. Calcium hydride, and especially lithium aluminum hydride, are much more expensive materials than sodium hydride. For many uses of silane it is desirable that the product silane be essentially free of halogenated silanes including unreacted silicon tetrafluoride.